Tip: Configuring network aliases with NetworkManager on Fedora 14

Linux supports the concept of “network aliases”; a NIC with more than one IP-address.

Previously, with networking managed by /etc/init.d/network, you would create a configuration file (/etc/sysconfig/network-scripts/ifcfg-eth0:0) holding the IP-address information for alias “0” of network interface “eth0“.

With NetworkManager, things become more complicated for non-trivial network configurations. The primary interface settings are in /etc/sysconfig/network-scripts/ifcfg-eth0 as usual:

  DEVICE="eth0"
  NM_CONTROLLED="yes"
  ONBOOT=yes
  HWADDR=00:04:23:C0:FF:EE
  TYPE=Ethernet
  BOOTPROTO=dhcp
  DEFROUTE=yes
  PEERDNS=yes
  PEERROUTES=yes
  IPV4_FAILURE_FATAL=yes
  IPV6INIT=no
  NAME="System eth0"
  UUID=5fb06bd0-0bb0-7ffb-45f1-deadbeefc0ffee

Based on a comment by Cristiano, I added a script to NetworkManager that would take care of configuring any network aliases that might be defined:

  $ cat /etc/NetworkManager/dispatcher.d/00-aliases
  #!/bin/bash
  # Based on comment by Cristiano, http://mihai.ibanescu.net/networkmanager-and-virtual-interfaces
  
  iface="$1"
  shift
  action="$1"
  shift
  
  if [ "$action" = "up" ]; then
    for ALIAS in /etc/sysconfig/network-scripts/ifcfg-$iface:*; do
      ALIAS=`echo $ALIAS | cut -d: -f 2`
      /sbin/ifup $iface:$ALIAS
    done
  fi
  # EOF

Note: This script needs to be executable.

The alias settings are configured in /etc/sysconfig/network-scripts/ifcfg-eth0:0

  DEVICE="eth0:0"
  NM_CONTROLLED="no"
  BOOTPROTO=static
  IPADDR=172.16.0.1
  NETMASK=255.255.0.0

The essential ingredient here is “NM_CONTROLLED=no” (thanks to IRC @so_solid_moo, #fedora). Without that setting, NetworkManager will treat your alias as a real device and mess up your network accordingly ;-)